The present invention relates generally to compass systems, and more particularly, to a flexure plate capacitive compass.
It is well known that aerospace systems, such as missile systems, require internal control systems for the purpose of maintaining a particular level or attitude with respect to a fixed frame, such as the earth.
Currently, mechanical gyro-compass systems are used in aerospace systems to determine earth-spin direction and rotating beam pointing directions. In other words, gyro-compasses find North by using an (electrically powered) fast spinning wheel and friction forces in order to exploit the rotation of the earth. Resultantly, gyro-compasses typically require large amounts of energy to maintain spinning motion.
Minimizing energy requirements is a constant goal for aerospace systems, therefore either eliminating or powering down mechanical gyro-compasses after direction is established would thereby dramatically decrease power consumption.
As was mentioned, compass systems are used in aerospace or in a portion of aircraft or spacecraft navigation or guidance systems. During operation of those system types, the operating environment temperature changes over a wide range. Consequently, object orientations must be measured and controlled with a high accuracy over a wide range of temperatures and temperature gradients. This is often a difficult and inefficient process.
The disadvantages associated with current compass systems have made it apparent that a new compass system is needed. The new compass system should minimize gyro-compass usage, substantially minimize temperature sensing requirements, and should also improve compass accuracy. The present invention is directed to these ends.
In accordance with one aspect of the present invention, a compass system includes a platform defining an xy-plane, wherein a z-axis is orthogonal to the xy-plane. A beam is rotatably coupled to the platform such that the beam rotates about the y-axis. An accelerometer including a flexure plate perpendicular to the rotating beam is coupled to the beam a distance from the y-axis. The accelerometer generates an accelerometer signal in response to movement of the flexure plate. An angular position sensor senses angular position of the beam relative to the x-axis in the xy-plane, the angular position sensor generating an angular position signal therefrom. A processor receives the accelerometer signal and the angular position signal and generates an East-West signal therefrom.
In accordance with another aspect of the present invention, a method for operating a compass system on the earth includes leveling a platform with respect to local earth gravity; rotating a flexure plate bridge accelerometer in a plane perpendicular to the platform such that the flexure plate bridge accelerometer reads a sum of a radial acceleration due to the beam rotation, the rotation of the earth, and gravity; generating a sinusoidal signal of a rotating acceleration of the flexure plate bridge accelerometer due to the sum of the velocity of the accelerometer and the rotation of the earth and gravity; reading a positive peak and a negative peak within the sinusoidal signal; and generating an earth rate direction signal in response to the positive peak and the negative peak. As the beam is rotated about the y-axis, the amplitude of the sine wave will vary as to the cosine of the angle formed by the beam and the earth spin vector.
One advantage of the present invention is that it generates a dynamic range and granularity sufficient for Inter-Continental Ballistic Missile (ICBM) usage. Additional advantages include that the compass system consumes less power than prior compass systems, while dramatically improving reliability and reduction in manufacturing costs.
Additional advantages and features of the present invention will become apparent from the description that follows, and may be realized by means of the instrumentalities and combinations particularly pointed out in the appended claims, taken in conjunction with the accompanying drawings.